1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a CMOS amplifier of a filter, and more particularly, a CMOS amplifier and a method of the same for applying to a filter, for example, a Low Pass Filter (LPF), having a high voltage gain and a high gain-bandwidth product, for ultra wideband application.
2. Description of Related Art
Recently, together with development of a system for transmitting and receiving high speed wireless data, such as a mobile phone, a Digital Multimedia Broadcasting (DMB) phone, a personal digital assistant (PDA), an ultra wideband (UWB) system and the like, a high gain/wideband CMOS amplifier is required for operation of the system. As an example, an integrator and a Low Pass Filter (LPF), as shown in FIG. 1, may adopt a CMOS amplifier as an operational amplifier AMP together with a resistor R and a capacitor C and the like. Also, a CMOS amplifier may be broadly utilized in many devices, such as a High Pass Filter (HPF), a Band Pass Filter (BPF), an oscillator, a mixer and the like.
Particularly, in a UWB system using a Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) scheme, an LPF, which may cover a high voltage, for example, about 200 mV peak-to-peak, and having about a 235 MHz cutoff frequency, is needed for processing a Radio Frequency (RF) signal. Normally, a differential amplifier, generating an output VOUT by amplifying a differential input VIN when provided in the same structure as shown in FIG. 2, is utilized for an LPF and the like. Various techniques such as adding an additional circuit to the differential amplifier in order to process an ultra wideband signal have been developed.
Techniques such as an active R-C filter, a Gm-C filter, a metal-oxide semiconductor field effect transistor (MOSFET)-C filter, an Operational Transconductance Amplifier (OTA) and so on, for a high gain and a wideband system, have been widely developed. However, more research may be required to effectuate a high linearity in an ultra wideband system such as an MB-OFDM system.